Light Emitting Diode Driving System

1. A light emitting diode (LED) driving system, to drive a plurality of LED strings, wherein the LED driving system comprises: a converter, to convert an external power signal into a direct current power signal able to drive the LED strings; a controller, to control the converter to output the direct current power signal; a plurality of current limitation circuits, correspondingly connected to the LED strings, wherein each of the current limitation circuits comprises: a first switch, comprising a control pole, a first pole, and a second pole, the control pole connected to a reference voltage, the first pole connected to a corresponding LED string, and the second pole grounded via a first resistor; and a second switch, comprising a control pole, a first pole and a second pole, the control pole of the second switch connected to the second pole of the first switch via a second resistor, the first pole of the second switch connected to the control pole of the first switch, and the second pole of the second switch being grounded; and a plurality of over-voltage protection circuits correspondingly connected to the LED strings, wherein each of the over-voltage protection circuits comprises: a zener diode with a cathode connected to a corresponding LED string together with the first pole of the first switch; a third switch, comprising a control pole, a first pole and a second pole, the control pole of the third switch connected to an anode of the zener diode by way of a third resistor, the first pole of the third switch connected to the control pole of the first switch, and the second pole of the third switch being grounded; and a first capacitor, connected between the control pole of the third switch and the ground; wherein the control pole of the first switch, the first pole of the second switch and the first pole of the third switch all connect to the reference voltage via a fourth resistor.

2. The LED driving system of claim 1 , wherein the current limitation circuit further comprises a thermal element connected to the first resistor in parallel.

3. The LED driving system of claim 2 , wherein the thermal element is a negative temperature coefficient thermistor.

4. The LED driving system of claim 1 , wherein the first switch and the second switch are both bipolar junction transistors, the third switch is a transistor, the control poles of the first switch, the second switch and the third switch are all bases, the first poles of the first switch, the second switch and the third switch are all collectors, and the second poles of the first switch, the second switch and the third switch are all emitters.

5. The LED driving system of claim 1 , wherein the converter circuit comprises: an inductor, one end of the inductor receiving the external power signal; a fourth switch, connected to the other end of the inductor to convert the external power signal and comprising a control pole; and a rectification and filter circuit, connected between the other end of the inductor and the LED strings and connected to the fourth switch to rectify and filter the converted external power signal to the direct current power signal.

6. The LED driving system of claim 5 , wherein the rectification and filter circuit comprises: a diode, wherein an anode of the diode is connected to the other end of the inductor, and a cathode of the diode is connected to the LED strings; and a second capacitor, connected between the cathode of the diode and the ground.